As for the killer, from episode one I have believed and only believed that Mitch either killed her or was directly involved. Nothing she has done was helped to sway me in the slightest.

What makes you think that?

Obviously, I could be totally wrong and maybe it's because Michelle Forbes is perfection as a villain, but with Mitch's every move she seems to be haunted by guilt. Just how I interpret all her scenes.

I always took that to be guilt and regret for being a shitty parent unable to correct the past, rather than having a hand in her death. But with this show, anything is possible and/or a red herring.